How to change default sculpting color?
You can change the Viewport Shading in the top right corner of the 3D editor. Open up the drop-down menu by pressing the upside-down ^, then select MatCap. Then, press the ball to change which MatCap you want to use.



I believe this is the one you're seeing in the video.



Note that these settings will only be visible if you're in the Solid Viewport Shading mode.